24,768 research outputs found
Resonance bifurcations from robust homoclinic cycles
We present two calculations for a class of robust homoclinic cycles with
symmetry Z_n x Z_2^n, for which the sufficient conditions for asymptotic
stability given by Krupa and Melbourne are not optimal.
Firstly, we compute optimal conditions for asymptotic stability using
transition matrix techniques which make explicit use of the geometry of the
group action.
Secondly, through an explicit computation of the global parts of the Poincare
map near the cycle we show that, generically, the resonance bifurcations from
the cycles are supercritical: a unique branch of asymptotically stable period
orbits emerges from the resonance bifurcation and exists for coefficient values
where the cycle has lost stability. This calculation is the first to explicitly
compute the criticality of a resonance bifurcation, and answers a conjecture of
Field and Swift in a particular limiting case. Moreover, we are able to obtain
an asymptotically-correct analytic expression for the period of the bifurcating
orbit, with no adjustable parameters, which has not proved possible previously.
We show that the asymptotic analysis compares very favourably with numerical
results.Comment: 24 pages, 3 figures, submitted to Nonlinearit
Bidirectional ventricular tachycardia in cardiac sarcoidosis.
A 73-year-old man with history of pulmonary sarcoidosis was found to have runs of non-sustained bidirectional ventricular tachycardia (BVT) with two different QRS morphologies on a Holter monitor. Cardiac magnetic resonance delayed gadolinium imaging revealed a region of patchy mid-myocardial enhancement within the left ventricular basal inferolateral myocardium. An 18-fluorodeoxyglucose positron emission tomography (FDG-PET) showed increased uptake in the same area, consistent with active sarcoid, with no septal involvement. Follow-up FDG-PET one year later showed disease progression with new septal involvement. Cardiac sarcoidosis, characterized by myocardial inflammation and interstitial fibrosis that can lead to conduction system disturbance and macro re-entrant arrhythmias, should be considered in differential diagnosis of BVT. BVT may indicate septal involvement with sarcoidosis before the lesions are large enough to be detected radiologically
Phenomenology of the Flavor-Asymmetry in the Light-Quark Sea of the Nucleon
A phenomenological ansatz for the flavor-asymmetry of the light sea
distributions of the nucleon, based on the Pauli exclusion principle, is
proposed. This ansatz is compatible with the measured flavor-asymmetry of the
unpolarized sea distributions, , of the nucleon. A prediction
for the corresponding polarized flavor-asymmetry is presented and shown to
agree with predictions of (chiral quark--soliton) models which successfully
reproduced the flavor-asymmetry of the unpolarized sea.Comment: 5 pages, LaTeX, 2 figures, uses epsfi
Increased plasticity of the bodily self in eating disorders
Background: The rubber hand illusion (RHI) has been widely used to investigate the bodily self in healthy individuals. The aim of the present study was to extend the use of the RHI to examine the bodily self in eating disorders. Methods: The RHI and self-report measures of eating disorder psychopathology (EDI-3 subscales of Drive for Thinness, Bulimia, Body Dissatisfaction, Interoceptive Deficits, and Emotional Dysregulation; DASS-21; and the Self-Objectification Questionnaire) were administered to 78 individuals with an eating disorder and 61 healthy controls. Results: Individuals with an eating disorder experienced the RHI significantly more strongly than healthy controls on both perceptual (i.e., proprioceptive drift) and subjective (self-report questionnaire) measures. Furthermore, both the subjective experience of the RHI and associated proprioceptive biases were correlated with eating disorder psychopathology. Approximately 20% of the variance for embodiment of the fake hand was accounted for by eating disorder psychopathology, with interoceptive deficits and self-objectification significant predictors of embodiment. Conclusions: These results indicate that the bodily self is more plastic in people with an eating disorder. These findings may shed light on both aetiological and maintenance factors involved in eating disorders, particularly visual processing of the body, interoceptive deficits, and self-objectification
Simulation of a non-invasive charge detector for quantum cellular automata
Information in a Quantum Cellular Automata architecture is encoded in the
polarizazion state of a cell, i.e., in the occupation numbers of the quantum
dots of which the cell is made up. Non-invasive charge detectors of single
electrons in a quantum dot are therefore needed, and recent experiments have
shown that a quantum constriction electrostatically coupled to the quantum dot
may be a viable solution. We have performed a numerical simulation of a system
made of a quantum dot and a nearby quantum point contact defined, by means of
depleting metal gates, in a two-dimensional electron gas at a GaAs/AlGaAs
heterointerface. We have computed the occupancy of each dot and the resistance
of the quantum wire as a function of the voltage applied to the plunger gate,
and have derived design criteria for achieving optimal sensitivity.Comment: 8 pages, RevTeX, epsf, 5 figure
Polarization of Astronomical Maser Radiation. IV. Circular Polarization Profiles
Profile comparison of the Stokes parameters and is a powerful tool
for maser data analysis, providing the first direct methods for unambiguous
determination of (1) the maser saturation stage, (2) the amplification optical
depth and intrinsic Doppler width of unsaturated masers, and (3) the
comparative magnitudes of Zeeman splitting and Doppler linewidth. Circular
polarization recently detected in OH 1720 MHz emission from the Galactic center
appears to provide the first direct evidence for maser saturation.Comment: 14 pages, 1 Postscript figures (included), uses aaspp4.sty. To appear
in Astrophysical Journa
On the symmetry breaking phenomenon
We investigate the problem of symmetry breaking in the framework of dynamical
systems with symmetry on a smooth manifold. Two cases will be analyzed: general
and Hamiltonian dynamical systems. We give sufficient conditions for symmetry
breaking in both cases
Probing quark gluon plasma properties by heavy flavours
The Fokker Planck (FP) equation has been solved to study the interaction of
non-equilibrated heavy quarks with the Quark Gluon Plasma (QGP) expected to be
formed in heavy ion collisions at RHIC energies. The solutions of the FP
equation have been convoluted with the relevant fragmentation functions to
obtain the and meson spectra. The results are compared with
experimental data measured by STAR collaboration. It is found that the present
experimental data can not distinguish between the spectra obtained from
the equilibrium and non-equilibrium charm distributions. Data at lower
may play a crucial role in making the distinction between the two. The nuclear
suppression factor, for non-photonic single electron spectra
resulting from the semileptonic decays of hadrons containing heavy flavours
have been evaluated using the present formalism. It is observed that the
experimental data on nuclear suppression factor of the non-photonic electrons
can be reproduced within this formalism by enhancing the pQCD cross sections by
a factor of 2 provided the expansion of the bulk matter is governed by the
velocity of sound, . Ideal gas equation of state fails to
reproduce the data even with the enhancement of the pQCD cross sections by a
factor of 2.Comment: Minor modification of tex
Transition to subcritical turbulence in a tokamak plasma
Tokamak turbulence, driven by the ion-temperature gradient and occurring in
the presence of flow shear, is investigated by means of local, ion-scale,
electrostatic gyrokinetic simulations (with both kinetic ions and electrons) of
the conditions in the outer core of the Mega-Ampere Spherical Tokamak (MAST). A
parameter scan in the local values of the ion-temperature gradient and flow
shear is performed. It is demonstrated that the experimentally observed state
is near the stability threshold and that this stability threshold is nonlinear:
sheared turbulence is subcritical, i.e. the system is formally stable to small
perturbations, but, given a large enough initial perturbation, it transitions
to a turbulent state. A scenario for such a transition is proposed and
supported by numerical results: close to threshold, the nonlinear saturated
state and the associated anomalous heat transport are dominated by long-lived
coherent structures, which drift across the domain, have finite amplitudes, but
are not volume filling; as the system is taken away from the threshold into the
more unstable regime, the number of these structures increases until they
overlap and a more conventional chaotic state emerges. Whereas this appears to
represent a new scenario for transition to turbulence in tokamak plasmas, it is
reminiscent of the behaviour of other subcritically turbulent systems, e.g.
pipe flows and Keplerian magnetorotational accretion flows.Comment: 16 pages, 5 figures, accepted to Journal of Plasma Physic
Tuning Monte Carlo Generators: The Perugia Tunes
We present 9 new tunes of the pT-ordered shower and underlying-event model in
PYTHIA 6.4. These "Perugia" tunes update and supersede the older "S0" family.
The data sets used to constrain the models include hadronic Z0 decays at LEP,
Tevatron minimum-bias data at 630, 1800, and 1960 GeV, Tevatron Drell-Yan data
at 1800 and 1960 GeV, and SPS min-bias data at 200, 546, and 900 GeV. In
addition to the central parameter set, called "Perugia 0", we introduce a set
of 8 related "Perugia Variations" that attempt to systematically explore soft,
hard, parton density, and colour structure variations in the theoretical
parameters. Based on these variations, a best-guess prediction of the charged
track multiplicity in inelastic, nondiffractive minimum-bias events at the LHC
is made. Note that these tunes can only be used with PYTHIA 6, not with PYTHIA
8. Note: this report was updated in March 2011 with a new set of variations,
collectively labeled "Perugia 2011", that are optimized for matching
applications and which also take into account some lessons from the early LHC
data. In order not to break the original text, these are described separately
in Appendix B. Note 2: a subsequent "Perugia 2012" update is described in
Appendix C.Comment: 46 page
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